1. Field of the Invention
The present invention relates, in general, to air conditioning systems for vehicles and more particularly to air conditioning systems for vehicles with engines which produce heat as they provide mechanical work.
2. Description of the Prior Art
In the past, air conditioners used on vehicles such as cars and trucks have not been entirely satisfactory. A particular problem with these air conditioners has been that the elements of the air conditioner are located in a heated environment, namely the engine compartment. The heat from the engine heats the elements of the air conditioner and makes the cooling provided by the air conditioner less efficient.
This is especially true when the outside temperature is higher than normal making the engine compartment hotter than normal. Of course, when the outside temperature is greater, the need for cooling the car interior by an air conditioner is also greater. This causes the air conditioner to be least efficient when the need for the cooling from the air conditioner is greatest. This inefficiency in turn causes a greater load to be placed on the car engine further heating the engine and increasing the inefficiency of the air conditioner. The load placed on a vehicle's engine to operate these inefficient air conditioners has led to reduced available engine power and increased gasoline consumption by the engines. This loss in horsepower is significant when air conditioners are used on small vehicles designed with low horsepower engines for gasoline savings. Further, this loss in horsepower for a small vehicle can be hazardous for passing and pulling loads to the extent that air conditioners are not recommended in small vehicles.
While absorption type air conditioning and heating systems utilizing low temperature energy sources are known, usually these systems are too heavy and too large to be used in a vehicle.
One engine cooling system and air conditioning system is shown in U.S. Pat. No. 4,164,850 to Lowi. This patent describes a new type of cooling system for a car engine combined with a a low temperature heat engine air conditioning system. The engine cooling system comprises engine and exhaust manifold jackets through which a refrigerant (such as freon) is circulated. This refrigerant fluid is conducted in four different paths, depending on the mode of the system, to achieve either fast heating of the engine, air conditioning of the car with cooling of the engine, heating of the car with cooling of the engine, or cooling of the engine alone. In the mode for air conditioning of the car and cooling of the engine, refrigerant is heated in the engine and exhaust manifold jackets. This heated refrigerant is then conveyed through an ejector which induces flow of this refrigerant in a low pressure evaporation air conditioning cycle. Some of the refrigerant is then repressurized by a pump and circulated for heating to the engine and exhaust jackets.
As can be seen, the Lowi patent describes an air conditioning system which replaces the conventional water cooling system of a car with a refrigerant circulated through engine and exhaust jackets. Moreover, this system requires at least four circulation modes to allow heating, cooling and neither heating or cooling to occur while not overheating the engine. Of course, if a freon leak occurs (which is much more likely than a water leak because freon is gaseous and must be held under pressure at room temperature) loss of the ability to cool the engine occurs as well. There are several serious disadvantages to the system described in the Lowi patent which are due to circulation of hydrocarbon type refrigerants directly through the engine block and exhaust manifold jackets. The refrigerant in Lowi's system could become contaminated with oil, grease, fine metal fragments and other materials from the engine. Prolonged contact of the refrigerant in the presence of even low levels of moisture at the elevated surface metal temperatures of the exhaust manifold and engine would degrade hydrocarbon refrigerants. The presence of these jackets would also increase access and maintenance problems when the engine needed repair or servicing. Also a large volume around the engine would be taken up by the jackets since the jackets would have to be large enough to provide the necessary heat transfer area to remove heat from the engine.